In a conventional turbine compressor component, rotor blades are held in a rotor blade wheel by means of a dovetail connection, i.e., a dovetail on the blade is received in a complimentary dovetail slot in the wheel.
The fit between the blade and the dovetail slot in the rotor wheel is loose to allow for assembly and tolerances. Therefore, if the blades are not properly retained, the loose fit may allow the hardware to move in the slot, leading to excessive wear. The excessive wear could eventually fail the part, requiring the unit to be shut down until a repair can be made.
Typically, each rotor blade is retained in the blade wheel to limit motion along the ring dovetail slot by one or more stakes. This is a process where material at the edge of the wheel slot is plastically deformed and displaced into a void created by a local chamfer of the blade dovetail. This is a manual and highly variable process which can in some cases provide inadequate retention of the rotor blade in the rotor wheel slot. Vibratory forces acting on the rotor can produce wear on the stake leading to eventual failure of the retention feature. Once the stake is worn, the blade can then slide freely in the wheel slot. At very high amplitudes, this motion can lead to wearing of the blade dovetail and eventual failure. This could then lead to blade liberation and subsequent collateral damage to the gas turbine. There have also been many documented instances of rotor blades being installed incorrectly by, for example, inserting the blade in the wheel slot backwards. Some of these mis-assemblies have been identified as causes of subsequent failure of machine equipment.
There remains a need for a field-retrofittable blade retention mechanism that will allow the blade to be installed, removed and reinstalled without damaging the blades or the wheel.